The present invention relates to a printer comprising: a frame, a bearing assembly mounted to the frame, a platen rotatably supported in the bearing assembly for advancing a sheet of a recording medium, a guide rail mounted to the frame and extending in parallel with the axial direction of the platen, a ruler extending in parallel with the guide rail, a carriage driven to reciprocate along the guide rail, said carriage carrying a printhead, and a detector arranged to detect the position of the carriage relative to the ruler.
A typical example of a printer of this type is an ink jet printer having a printhead or printheads adapted to expel droplets of liquid ink onto the recording medium that is advanced over the platen. The timings at which the nozzles of the printhead are energized must be accurately synchronized with the movement of the carriage. To this end, the carriage is equipped with a detector for reading markings on the ruler. In order to achieve a high print quality, it is a prerequisite that the position of the ruler relative to the recording medium in the direction of the reciprocating movement of the carriage is stable over the whole print process.
In a conventional printer, the ruler is fixed at the guide rail, and the frame has a very stiff construction so that it will not be distorted by forces of inertia that are created by the acceleration and deceleration of the carriage.